In the automotive field, rolling element bearing assemblies are vital components in the numerous components of a vehicle.
Low friction operation and reliability are two of the key attributes for the selection of specific bearing assemblies. Another important factor is the ease of installation of the bearing assembly on a shaft. In one application, powered strut assemblies are used to support vehicle body panels such as rear hatch backs of the van and SUV type vehicles. In one design for such components the strut provides both weight balancing spring biasing as well as incorporating in an internal motor actuator for remote controlled movement of the body panels. These devices have one or more rolling element bearings supported within a hollow tube and support a rotatable shaft at the center of the tube. The rotatable shaft may be integrally formed with a threaded spindle that cooperates with a spindle nut to translate the shaft rotation into a linear movement of a part coupled to the spindle nut.
A typical rolling element type bearing assembly includes an inner race and an outer race with rolling bearing elements therebetween. In one application, for example the above-mentioned vehicle strut assembly, the inner race is locked to and rotates with a shaft. A separate outer race is fixedly connected to a supporting structure, such as the equipment framework or body or a strut tube. Smooth and efficient rotary motion of the inner race relative to the fixed outer race is achieved by a plurality of bearing elements, such as rollers or balls.
Several arrangements exist for mounting and locking the inner race of a bearing to a shaft, such as press fitting. In order to secure the inner race of the bearing to the shaft by press fitting, first the shaft is manufactured with a slightly oversized cross-sectional diameter as compared to the diameter of the inner race. The shaft is then forcibly fit into the inner race to effect the tight frictional engagement therewith.
Locking the inner race of the bearing to the shaft through press fitting has several shortcomings. In order to effectively lock the inner race and shaft together, these parts must be machined to very close tolerances, often within a few ten-thousandths of an inch. It is sometimes even necessary to heat the inner race of the bearing to cause it to temporarily expand to make it easier to slip over the end of the shaft. In these ways, and in other ways, such limitations result in more expensive bearing component and bearing assembly manufacturing costs.
Alternative arrangements may include clamp rings that axially secure the inner race on the shaft by engaging with grooves formed in the shaft on both axial sides of the inner race. Such clamp rings may be resilient so as to be snapped into the grooves. Because the snap rings and the grooves are premanufactured, they cannot compensate for manufacturing tolerances.
There is a continuing need for bearing shaft assemblies that are reliable and precise, while at the same time easy to manufacture at a low cost.